I have a student that has analyzed and optimized Simpson. We came up with a formula that will let you solve for the optimal base diameter, max arm length, or mechanical advantage given the other two assume normal design constraints of a 3D printer. I will be sure to link the paper here once he finalizes it. For now, check out the attached STL that represents the whole print volume of a Simpson where the speed and precision are acceptable. I would include a picture but they don't do it justice. You really need to open it up and rotate the view.

PS Great work to all of you pushing on without me. I have to get through another semester of grad school and then I plan to jump back in.